Accretion onto black holes probably powers many bright astrophysical sources such as active galactic nuclei, some stellar-mass x-ray sources, gamma-ray bursts, and relativistic radio jets. I will survey developments in the theory of black hole accretion, with a particular focus on those relevant to the Event Horizon Telescope experiment, a global millimeter-wavelength interferometer that is attempting to image hot plasma near black holes on the scale of the event horizon.